KR100389072B1 - Optical pick-up device - Google Patents

Optical pick-up device Download PDF

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Publication number
KR100389072B1
KR100389072B1 KR10-1996-0003593A KR19960003593A KR100389072B1 KR 100389072 B1 KR100389072 B1 KR 100389072B1 KR 19960003593 A KR19960003593 A KR 19960003593A KR 100389072 B1 KR100389072 B1 KR 100389072B1
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KR
South Korea
Prior art keywords
light
recording medium
optical recording
optical
convex lens
Prior art date
Application number
KR10-1996-0003593A
Other languages
Korean (ko)
Other versions
KR960032345A (en
Inventor
겐지 야마도또
후미사다 마에다
이사오 이찌무라
기요시 오사또
도시오 와따나베
Original Assignee
소니 가부시끼 가이샤
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Priority to JP02656395A priority Critical patent/JP3567515B2/en
Priority to JP95-026563 priority
Application filed by 소니 가부시끼 가이샤 filed Critical 소니 가부시끼 가이샤
Publication of KR960032345A publication Critical patent/KR960032345A/en
Application granted granted Critical
Publication of KR100389072B1 publication Critical patent/KR100389072B1/en

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B82NANOTECHNOLOGY
    • B82YSPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1372Lenses
    • G11B7/1374Objective lenses
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1392Means for controlling the beam wavefront, e.g. for correction of aberration
    • G11B7/13925Means for controlling the beam wavefront, e.g. for correction of aberration active, e.g. controlled by electrical or mechanical means
    • G11B7/13927Means for controlling the beam wavefront, e.g. for correction of aberration active, e.g. controlled by electrical or mechanical means during transducing, e.g. to correct for variation of the spherical aberration due to disc tilt or irregularities in the cover layer thickness
    • GPHYSICS
    • G11INFORMATION STORAGE
    • G11BINFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only

Abstract

There is provided an optical pickup apparatus capable of removing spherical aberration due to thickness error of an optical disk. The optical pickup apparatus comprises: a convex lens having a plane facing the surface of the optical recording medium and having a predetermined refractive index; An objective lens disposed so as to sandwich a convex lens between the optical recording medium and the objective lens; A condensing optical system for condensing light reflected from the light incident surface of the optical recording medium and the plane of the convex lens; First light detection means for detecting light passing through the light-converging optical system reflected from the light incident surface of the optical recording medium to generate a first detection signal; Second light detecting means for detecting light passing through the light-converging optical system from the plane of the convex lens and generating a second detection signal; Position detecting means for detecting a positional relationship between the light incident surface of the optical recording medium and the plane of the convex lens on the basis of the first and second detection signals; Wherein the distance between the light incident surface of the optical recording medium and the plane of the convex lens is set to be larger than a distance between the optical recording medium and the objective lens, And driving means for driving the convex lens along the optical axis.

Description

Optical pick-up device

The present invention relates to an optical pickup apparatus for condensing light projected from a light source on a signal recording surface of an optical recording medium such as an optical disc or the like.

In recent years, in the field of computer recording media and package media for recording audio and image information, high-density disk-type recording media and magneto-optical disks have been used. One method proposed to achieve such a high density recording medium is to increase the numerical aperture of the objective lens used in the optical pickup apparatus and to reduce the spot size (diameter) of the focused light on the signal recording surface of the optical disk Method.

For example, in the case where a densified information signal already recorded on an optical disc in the form of information pits is read by the optical pickup device, the spot size of the read beam is made as small as possible so that a pit formed as a fine recording mark on the optical disc By reproducing the information, high-density recording can be achieved.

Incidentally, as the numerical aperture of the objective lens used in the optical pickup apparatus becomes larger, it becomes difficult to manufacture the objective lens itself, and the manufacturing cost is increased.

In addition, when the thickness of the optical disc described above deviates from a predetermined value, spherical aberration occurs. The spherical aberration W 40 is expressed by the following equation (1).

Here,? T represents the thickness error of the optical disk, N represents the refractive index, and NA represents the aperture value.

As can be seen from equation (1), the spherical aberration W 40 is proportional to the numerical aperture NA. That is, as the aperture value increases, an increased spherical aberration is likely to occur. Therefore, the thickness of the optical disc must be strictly controlled. However, control over such optical disc thickness is disadvantageous as a result of low productivity and high manufacturing cost.

Accordingly, an object of the present invention is to provide a magneto-optical recording medium which exhibits a high aperture value of an objective lens used therein and achieves a small spot size of a read / write light beam condensed on an optical recording medium to realize high density recording, And an optical pickup device capable of reducing spherical aberration caused by an error.

According to the present invention, there is provided an optical recording medium comprising: a convex lens having a plane opposite to a light incident surface of an optical recording medium and having a predetermined refractive index; An objective lens disposed so as to sandwich a convex lens between the optical recording medium and the objective lens; A condensing optical system for condensing light reflected from the light incident surface of the optical recording medium and the plane of the convex lens; First light detecting means for detecting light passing through the light-converging optical system reflected from the light incident surface of the optical recording medium to generate a first detection signal; Second light detecting means for detecting light passing through the light-converging optical system from the plane of the convex lens to generate a second detection signal; Position detecting means for detecting a positional relationship between a light incident surface of the optical recording medium and a plane of the convex lens on the basis of the first and second detection signals; The first and the first detection signals are set so that the distance between the light incident surface of the optical recording medium and the plane of the convex lens is controlled by allowing the convex lens to move in the opposite direction along the optical axis toward the optical recording medium or the objective lens. And driving means for driving the convex lens to the optical recording medium, wherein an optical pickup device for condensing the light beam projected from the light source onto the optical recording medium is provided.

In this case, the first light detecting means is disposed at a position corresponding to the conjugate point of the reflected light from the light incident surface of the optical recording medium to the light-converging point, and the second light- And is disposed at a position corresponding to a conjugate point with respect to the light-converging point of the reflected light.

Therefore, in the optical pickup apparatus according to the present invention, since the convex lens having a given refractive index is disposed between the objective lens and the optical recording medium, the total numerical aperture of the optical system can be increased. In addition, since the positional relationship between the light incident surface of the optical recording medium and the plane of the convex lens is determined in accordance with the detection signal from the light detecting means, the distance therebetween can be well controlled. Therefore, the spherical aberration occurring on the signal recording surface of the optical recording medium is considerably reduced, and the reproducing characteristic of the optical recording medium can be increased.

Hereinafter, a preferred embodiment of the optical pickup device according to the present invention will be described with reference to the drawings.

The optical pickup apparatus according to the present invention performs a function of reproducing a densified information signal already recorded on the signal recording surface of the optical recording medium 20 such as an optical disk or the like. 1, the optical pick-up apparatus comprises a hemispherical lens 7 (convex lens) having a given refractive index and having a plane 7b opposite to the light incident surface 20a of the optical disc 20, A condensing optical system 23 for condensing the reflected light from the light incident surface 20a of the recording medium 20 and the plane 7b of the hemispherical lens 7 and the light incident surface 20a as the first light detecting means, (Hereinafter simply referred to as " PD ") that detects the light R2 that is reflected from the condensing optical system 23 and detects the light R2 passing through the condensing optical system 23, Based on the detection outputs Pb and Pc of the first and second PDs 15 and 19, the second PD 19 for detecting the light R3 that is reflected from the first condensing optical system 7b and passes through the condensing optical system 23, A subtracter 21 for detecting a positional relationship between a light incident surface 20a of the optical recording medium 20 and a plane 7b of the hemispherical lens 7, a light incident surface 20a of the optical recording medium 20, And hemisphere The optical recording medium 20 or the objective lens 6 is controlled based on the output Pb-Pc of the subtractor 21 to control the distance of the air layer (air gap) AG between the plane 7b of the lens 7, And an actuator 31 for driving the hemispherical lens 7 along its optical axis in a direction opposite to the direction of the optical axis.

In this case, the PD 15 is arranged at a position corresponding to a conjugate point with respect to the light-converging point of the light reflected from the light incident surface 20a of the optical recording medium 20 and passing through the condensing optical system 23 While the PD 19 is disposed at a position corresponding to the conjugate point with respect to the light-converging point of the light that is reflected from the plane 7b of the hemispherical lens 7 and passes through the condensing optical system 23. [ All of the PDs 15 and 19 are made up of, for example, four optical detectors and perform the function of detecting an error in the same way as when the astigmatism method is used. The detection output by the PD is applied to the subtractor 21 to detect the positional relationship between the light incident surface 20a of the optical recording medium 20 and the plane 7b of the hemispherical lens 7. [

Next, the detailed structure of the optical pickup device will be described below. The optical pickup apparatus includes a laser diode 1 as a light source, and a linearly polarized laser beam is emitted from the laser diode 1 toward the collimator lens 2. The laser beams passing through the collimator lens 2 are passed through in the form of parallel lines and diffracted through the deflection grating (diffraction grating) 3. The diffracted laser beam is also incident on the objective lens 6 after passing through a polarizing beam splitter 4 (hereinafter simply referred to as " PBS ") and a 1/4 wave plate 5, Passes through the hemispherical lens 7 toward the signal recording surface 20b of the recording medium (optical disk) 20. Incidentally, the laser beam to be focused on the signal recording surface 20b of the optical recording medium 20 is changed from linearly polarized light to circularly polarized light while passing through the 1/4 wave plate 5. [

The reflected light from the signal recording surface 20b of the optical recording medium 20 passes through the hemispherical lens 7 and the objective lens 6 and is incident on the 1/4 wave plate 5. The 1/4 wave plate 5 rotates the linearly polarized laser beam reflected from the signal recording surface 20b in the reverse direction so that the polarization direction of the laser beam after passing through the 1/4 wave plate 5 becomes the 1/4 wavelength plate To be converted into a 90 [deg.] Angle in the direction before it passes through the opening 5. Then, the rotated linearly polarized laser beam is incident on the PBS, where the rotated linearly polarized laser beam is reflected at an angle of 90 ° and proceeds toward the half mirror 8.

The half mirror 8 reflects 50% of the laser beam toward the condenser lens 9 and transmits the remaining 50% of the laser beam. Instead of the half mirror 8, a beam splitter having the same optical characteristics may be used. While passing through the condenser lens 9, the laser beam is condensed and travels toward the multi-lens 10, where the laser beam is further condensed on the photodetector 11.

The PBS 4, the half mirror 8, the condenser lens 9 and the multifocal lens 10 constitute one set of the half mirror 12, the condenser lens 13 and the multifocal lens 14, And constitutes a condensing optical system 23 together with a set of mirrors 16, a condenser lens 17 and a multi lens 18, the latter two sets of which will be described in detail below.

The photodetector 11 is composed of four separate optical detectors, whose outputs are applied to a reproduction processing unit (not shown) to generate an RF signal to calculate reproduced data, a tracking error signal, and a focusing error signal. In the reproduction processing unit, the RF signal is binarized, and then the binarization data thus obtained is subjected to the EFM demodulation processing and the CTRC decoding processing, so that reproduced data is obtained from the RF signal. The tracking error signal and focusing error signal are applied to a servo circuit (not shown). This servo circuit performs tracking control and focusing control based on the tracking error signal and focusing error signal using a two-axis actuator.

As shown in FIG. 2, the hemispherical lens 7 can be manufactured by cutting a part of the spherical lens 30. The cut surface of the hemispherical lens 7 is mirror-polished to form a plane 7b. The spherical lens 30 may be made of a material having the same refractive index as the light transmitting layer of the optical recording medium 20. [

The numerical aperture (NA) of the objective lens 6 is expressed by the following equation.

Where? Is 1/2 of the aperture angle of the outgoing light from the objective lens, and n is the refractive index of the optical transmission medium. In this case, the refractive index of the hemispherical lens 7 is set to 1.5, which is equal to the refractive index of the light-transmitting layer of the optical recording medium 20, for example. Therefore, the total aperture value of the optical pickup apparatus is 1.5 times the aperture value of a conventional optical pickup apparatus for focusing a laser beam passing through a transmission medium having a refractive index of 1 using only the objective lens. Therefore, the spot size of the laser beam on the signal recording surface 20b is set to 1 / 1.5, and high-density recording can be realized.

On the other hand, in order to prevent sliding friction between the plane 7a of the hemispherical lens 7 and the light incident surface 20a of the optical recording medium 20 when driving the optical recording medium 20, an air layer air gap AG is formed.

3 shows details of the interrelation between the air layer AG, hemispherical lens 7, optical recording medium 20 and objective lens 6. The hemispherical lens 7 is supported on the first holder 31. A first drive coil 32 is fixedly mounted to the first holder 31. [ On the other hand, the objective lens 6 is supported by the second holder 33 to which the magnet 34 is fixedly attached. The first holder 31 is movably supported by the leaf spring 35 on the second holder 33. [ That is, the mutual effect between the magnetic flux of the magnet 34 and the drive of the first drive coil 32 allows the hemispherical lens 7 and the objective lens 6 to independently move in the direction of the optical axis. The objective lens 6 is driven by the electromagnetic field effect between the second drive coil 36 fixed to the second holder 33 and the magnet 37. When the width of the air layer AG in the thickness direction of the optical recording medium 20 is changed, spherical aberration occurs. This spherical aberration (W '40) is expressed by the food (2).

Where h is the variation of the thickness of the air layer AG, n is the combined refractive index of the optical recording medium 20 and the hemispherical lens 7, and sin &thetas; is its combined aperture value.

As the spherical aberration (W '40) represented by the formula (2) becomes large, when the information signal recorded on the optical recording medium 20 is read by the optical pick-up apparatus, the reproduction characteristics are presented largely with decreased do.

In the optical pickup apparatus according to preferred embodiments of the invention, the formula (2), the spherical aberration (W '40) represented by the second holder 31, the first driving coil 32, magnet 34 and plate And is limited to a minimum level by using an actuator for a hemispherical lens composed of a spring 35. [ The hemispherical lens actuator controls the thickness of the air layer AG with high precision by driving the hemispherical lens toward the optical recording medium 20 or the objective lens 6 along its optical axis.

Next, the structure and operation principle of the optical pickup device according to the present invention will be described with reference to FIG. 4, the reflected light from the optical recording medium 20 is reflected by the first reflected light component R1 from the signal recording surface 20b, the second reflected light component R2 from the light incident surface 20a, And a third reflected light component R3 from the plane 7b of the lens 7. [ The first reflected light component R1 is incident on the PD 11 as shown in FIG.

Only 50% of the second reflected light component R 2 is transmitted through the half mirror 8. Also, only half of the 50% of the second reflected light component R2 can be transmitted through the half mirror 12 and incident on the PD 15. These half mirrors can be replaced by beam splitters. Similarly, only 50% of the third reflected light component R3 is transmitted through the half mirror 8, and only 50% of the third reflected light component R3 is transmitted through the half mirror 12 . A part of the third reflected light component R 3 reflected on the half mirror 12 is incident on the mirror 16 side where the total reflection of the third reflected light component R 3 takes place so that the third reflected light component R 3 Is incident on the PD 19 through the condenser lens 17 and the multi-lens 18. The PDs 15 and 19 are constituted identically by four separate light detectors. The multi-lenses 10, 14 and 18 are each composed of a cylindrical lens and a condenser lens as used in the astigmatism method.

The PD 15 detects the output of the second reflected light component R2 from the light incident surface 20a of the optical recording medium 20. [ In this case, the output to be detected is the same as that used in the astigmatism method. Likewise, the PD 19 also detects the output of the third reflected light component R3 equal to the output as used in the astigmatism method. The subtractor 21 performs subtraction of the detection output Pc of the PD 19 from the detection output Pb of the PD 15. [ The difference signal Pb-Pc thus obtained is applied to the driver 22, from which the difference signal is also applied to the drive coil 32 of the hemispherical lens actuator.

Each of the PDs 11, 15, and 19 is disposed at a position preliminarily adjusted according to the light-converging point of each of the first, second, and third reflected light components R1, R2, and R3. In FIG. 5, the optical paths of the first to third reflected light components R1 to R3 are indicated on the same optical axis in an overlapping form for the sake of clarity .

The PD 11 is disposed at a position corresponding to the conjugate point fa with respect to the light-converging point Fa on the signal recording surface 20b of the optical recording medium 20. [ The position of the conjugate point fa with respect to the light-converging point Fa is determined by the arrangement of the PBS 4, the half mirror 8, the condenser lens 9 and the multi-lens 10 sandwiched therebetween. At the same time, the PD 15 is disposed at a position corresponding to the conjugate point fb with respect to the light-converging point Fb of the second reflected light component R2 from the light incident surface 20a of the optical recording medium 20 . The position of the conjugate point fb with respect to the light-converging point Fb is determined by the arrangement of the PBS 4, the half mirror 8, the condenser lens 13 and the multi-lens 14 sandwiched therebetween. In addition, the PD 19 is disposed at a position corresponding to the conjugate point fc with respect to the light-converging point Fc of the third reflected light component R3 from the plane 7b of the hemispherical lens 7. The position of the conjugate point fc with respect to the light-converging point Fc is determined by the arrangement of the PBS 4, the half mirrors 8 and 12, the mirror 16, the condenser lens 17 and the multi- .

Specifically, the focus of the objective lens 6 is controlled by the PD 11 by using the astigmatism method. At this time, the focusing bias is set to zero. When the hemispherical lens 7 gradually approaches the optical recording medium 20 while the focus state is maintained, the PDs 15 and 19 detect the S-type signal outputs Pb and Pc of the reflected light components, respectively. The two S-type signal outputs (Pb, Pc) are electrically controlled so that their amplitudes, that is, the widths of the peaks and the peaks, coincide. The hemispherical lens 7 is fixed close to the position where the waveform of each of the two S-type signal outputs Pb and Pc intersects the zero point. The Z-lengths of the multi-lens 14 and the multi-lens 18 are respectively aligned with each other so that the output Pb of the PD 15 and the Z- The output Pc of the PD 19 becomes zero. The alignment of the Z-length of the multi-lenses 14 and 18 corresponds to the position of the light incidence surface 20a of the optical recording medium 20 and the plane 7a of the hemispherical lens 7 Means that the phases of the two S-type signal outputs from the PDs 15 and 19 are aligned with each other. Thus, the PDs 11, 15 and 19 are adjusted according to their positions.

Next, the control process for the air layer AG will be described below.

The outputs Pb and Pc of the PDs 15 and 19 are controlled such that the differential signal (Pb - Pc) becomes zero as a position detection signal from the subtracter 21 in order to keep the air layer AG constant do.

To this end, the position of the hemispherical lens 7 is adjusted by driving the driving coil 32 of the hemispherical lens actuator using the driver 22. [

The output Pb of the PD 15 and the output Pc of the PD 19 correspond to the positions of the light-converging points Fb and Fc for the objective lens 6, respectively. Particularly, when the light incident surface 20a of the optical recording medium 20 and the plane 7b of the hemispherical lens 7 are shifted from each other, the light-converging points Fb and Fc are also shifted from each other, The signal outputs Pb and Pc are correspondingly changed. At this time, if the thickness of the air layer AG does not change, the amount of movement of the light-converging point Fb, Fc with respect to the objective lens 6 coincides with each other so that the signal outputs Pb, Pc of the PDs 15, Gt; S-type < / RTI > signal output having a phase. Therefore, when the output (Pb - Pc) from the subtracter 21 becomes zero, it can be seen that the thickness of the air layer AG is kept constant. As a result, the difference signal (Pb - Pc) functions as a gap error signal.

Subsequently, a case where the air layer is changed will be described.

As shown in FIG. 6 (A, B), the output Pb of the PD 15 and the output Pc of the PD 19 are represented by S-shaped waveforms. The waveform of the output Pc of the PD 19 is shifted to the right in the waveform of the output Pb of the PD 15 as shown in Fig. 6 (A). On the other hand, when the thickness of the air layer AG becomes small, the waveform of the output Pc of the PD 19 is shifted leftward from the waveform of the output Pb of the PD 15 as shown in Fig. 6 (B) . Therefore, the gap error signal Pb-Pc calculated by the subtracter 21 changes as shown in FIG. 7. That is, when the thickness of the air layer AG becomes large, the gap error signal Pb - Pc becomes negative (-). On the other hand, when the thickness of the air layer AG becomes small, the gap error signal Pb - Pc becomes positive. Therefore, when the hemispherical lens 7 is driven by driving the driving coil 32 of the hemispherical lens actuator to reduce the gap error signal Pb - Pc, the thickness of the air layer AG can be kept substantially constant .

Therefore, according to the present invention, generation of spherical aberration can be prevented by controlling the air layer (air gap) AG between the hemispherical lens 7 and the optical recording medium (optical disc) 20 with high precision. As a result, a high reproduction characteristic for the optical recording medium can be realized.

On the other hand, commercially available optical discs inevitably show the thickness difference (thickness error) between them. Such thickness error also causes spherical aberration. According to the present invention, spherical aberration due to such a thickness error can be effectively prevented in the same manner.

Specifically, an electrical bias is applied to one of the PD 15 or the PD 19 to optimize the reproduction characteristic of the RF signal obtained from the detection output of the PD 11. As a result, the air gap AG corresponding to the electrical bias is generated, so that the air layer AG can be controlled with high precision. More specifically, such control is performed such that the spherical aberration caused by the thickness error of the optical disk is inversely proportional to the spherical aberration caused by the thickness error of the optical disk, so that the two spherical aberration cause the difference signals to be parallel to each other, . Therefore, even when the optical disc has a thickness error, the generation of spherical aberration can be eliminated by using the optical pickup device according to the present invention, so that excellent reproduction characteristics can be achieved.

FIG. 1 is a schematic view showing an optical pickup device according to a preferred embodiment of the present invention. FIG.

FIG. 2 is a view for explaining a manufacturing step of a convex lens used in the optical pickup device according to the present invention. FIG.

FIG. 3 is an enlarged view showing a detailed structure adjacent to a hemispherical ball-and-groove lens of an optical pick-up apparatus according to the present invention.

FIG. 4 is an enlarged view for explaining reflected light from the optical recording medium and the hemispherical convex lens.

FIG. 5 is a diagram showing a positional relationship between photodetectors as light detecting means according to a preferred embodiment of the present invention. FIG.

6 (A) and 6 (B) are graphs showing the relationship between the detection output for the reflected light from the hemispheric convex lens and the position of the hemispherical convex lens.

7 is a graph showing a relationship between a gap (air layer) between the optical recording medium and the hemispherical convex lens and a gap error signal for controlling such a gap.

DESCRIPTION OF THE REFERENCE NUMERALS

1. Laser diode 2. Collimator lens

3. Deflection grating 4. Polarizing beam splitter

5. 1/4 wave plate 6. Objective lens

7. Hemispherical Lenses 8,12. Half mirror

9, 13, 17. Converging lenses 10, 14, 18. Multilens

11. Photodetector 15. First photodetector (PD)

16. Mirror 19. The second photodetector (PD)

20. Optical recording medium (optical disc)

22. Driver 23. Condensing optical system

31. First holder 32. First drive coil

33. Second holder 34, 37. Magnet

35. Plate spring 36. Second drive coil

AG. Air layer

Claims (2)

  1. A convex lens having a plane facing the light incident surface of the optical recording medium and having a predetermined refractive index;
    The objective lens arranged to sandwich the convex lens between the optical recording medium and the objective lens;
    A condensing optical system for condensing light reflected from the light incident surface of the optical recording medium and the plane of the convex lens;
    First light detection means for detecting light passing through the light-converging optical system reflected from the light incident surface of the optical recording medium to generate a first detection signal;
    Second light detecting means for detecting light passing through the light-converging optical system from the plane of the convex lens and generating a second detection signal;
    Position detecting means for detecting a positional relationship between the light incident surface of the optical recording medium and the plane of the convex lens on the basis of the first and second detection signals;
    The distance between the light incident surface of the optical recording medium and the plane of the convex lens is controlled in accordance with the first and second detection signals by moving the convex lens in a direction opposite to the optical recording medium or the objective lens. Driving means for driving the convex lens along its optical axis;
    Wherein the optical pickup device is configured to focus the light incident from the light source onto the optical recording medium.
  2. The method according to claim 1,
    The first light detecting means is disposed at a conjugate point of light passing through the light converging optical system from the light incident surface of the optical recording medium with respect to the light converging point thereof, Is arranged at a conjugate point of light that is reflected from the plane of the convex lens and passes through the condensing optical system.
KR10-1996-0003593A 1995-02-15 1996-02-14 Optical pick-up device KR100389072B1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP02656395A JP3567515B2 (en) 1995-02-15 1995-02-15 Optical pickup device
JP95-026563 1995-02-15

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Publication Number Publication Date
KR960032345A KR960032345A (en) 1996-09-17
KR100389072B1 true KR100389072B1 (en) 2003-12-24

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US (1) US5712842A (en)
JP (1) JP3567515B2 (en)
KR (1) KR100389072B1 (en)
CN (1) CN1088884C (en)

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JP3567515B2 (en) 2004-09-22
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US5712842A (en) 1998-01-27
KR960032345A (en) 1996-09-17

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